Method of assembling motor vehicle body

ABSTRACT

A roof panel ( 31 ) is pre-set on the left and right side members ( 4 ) fixed to an underbody of a car. A roof panel spot welding station ( 7 ) includes a pair of frames ( 34 ) and two joisted-locating jigs ( 35, 36 ) bridging the frames. Each of the joisted-locating jigs is furnished with a clamp mechanism for holding the roof panel. The roof panel is located to the side members by the locating jigs, and spot-welded to the side members.

TECHNICAL FIELD

The present invention relates to a method of assembling a motor vehiclebody. Specifically, the present invention relates to a method forpre-fixing bridging parts, such as a roof panel, a header inner and aframe back, to the left and right side members, which are welded to anunderbody of a car.

BACKGROUND ART

A car body includes main parts such as an underbody, left and right sidemembers, and a roof panel. For assembling a car body using these parts,firstly the parts to be assembled are positioned relative to each other,using locating jigs, etc. Next, the parts are fixed by spot welding,thereafter re-spot welded to be fixed completely.

A conventional method of assembling a car body utilizes a significantlylarge locating jig for locating the main parts. For example, a jig usedto position the roof panel is larger than the roof panel itself. Suchlocating jig is installed above the car body assembly line and ismovable up and down. When pre-setting the roof panel on the left andright side members, the roof panel is transferred to a position belowthe locating jig, and set into the locating jig. Next, the locating jigis lowered to position both edges of the roof panel on the upper ends ofthe side members. Finally, in this manner, the roof panel is spot weldedto the side member.

The above-described conventional locating jigs for roof panel are largeand heavy, thus cause various problems. For example, conventional jigstend to require large facility investment at the beginning. Further, itis very complicated to replace the locating jigs corresponding to typesof cars to be manufactured. Specifically, the used locating jig shouldbe removed from a hoist and another jig should be set in thereto. Duringthis troublesome operation, the production line may be completelystopped.

Further, a motor for lifting the jig should bear a large load due to thelarge and heavy locating jig. Thus, a movable portion of the motor maysuffer trouble such as wear, so that constant maintenance is needed forworking the motor properly. Still further, it is difficult to performprecise location by using large and heavy locating jigs efficiently.

DISCLOSURE OF THE INVENTION

The present invention has been proposed under the above-describedcircumstances. It is therefore an object of the present invention torealize reduction in size and weight of the locating jig used for abridging part such as a roof panel, a header board and a frame back.

The present invention provides a method of assembling a car body by spotwelding a bridging part to a pair of side members fixed to an underbodyof a car. The method comprising the steps of: placing a pair of framesat sides of a transfer line for transferring the underbody and the sidemembers; attaching a plurality of detachable joisted-locating jigs tothe frame for locating the side member and the bridging part; and spotwelding the side members to the bridging part, with the side members andthe bridging part being clamped by the joisted-locating jigs. Anappropriate transfer system is employed to convey the joisted-locatingjig from the frame to a first stock area and to convey anotherjoisted-locating jig from a second stock area to the frame forperforming a joisted-locating jig change.

The joisted-locating jig can be made lighter and smaller thanconventional locating jig for roof panel. Thus, initial facilityinvestment may be reduced. Further, the joisted-locating jig accordingto the present invention does not obstruct the assembly operation evenif it is stored near the transfer line.

Preferably, the frame and the joisted-locating jig are positioned by aclamp mechanism.

Preferably, the transfer system includes a motor, a movable rail movedup and down by the motor, a fixed rail to be combined with the movablerail, and a pulley movable along the movable rail and the fixed rail.The joisted-locating jig is hung from the pulley.

Preferably, a sway prevention mechanism is provided for preventing themovable rail from swaying when the movable rail is apart from the fixedrail.

Preferably, the sway prevention mechanism includes a pair of verticalrods attached to the movable rail and a pair of fixed guides fixed toimmovable structure. The vertical rod moves relative to the fixed guidebe means of a roller.

Preferably, the movable rail is equipped with a fall-out preventiondevice, which is to prevent the pulley from falling out of the movablerail.

Preferably, the fall-out prevention device includes a stopper that turnson the pivot previously determined. The stopper is displaceable in thespan between engaging and disengaging points of the stopper and thepulley.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view illustrating a spot weldingstation for spot welding a side member of a car to an underbody.

FIG. 2 is a schematic plan view illustrating a structure of a car bodyassembly line.

FIG. 3 is a schematic view illustrating the underbody supported by twotransfer coasters, and the side member to be fixed to the underbody.

FIG. 4A is a schematic side view illustrating a roller conveyor fortransferring the underbody shown in FIG. 3.

FIG. 4B is a schematic side view illustrating an elevating mechanism foradjusting the height of the roller conveyor.

FIG. 5 is a schematic perspective view illustrating the coaster.

FIG. 6A illustrates an example where three locators are used for oneside member.

FIG. 6B is a section view taken along a line A-A in FIG. 6A.

FIG. 7 is a side view illustrating the side member at the spot weldingstation.

FIG. 8 is a schematic view illustrating a wheel installed on the locatorfor the side member, and a portion of a lifter on which the wheel isinstalled.

FIG. 9 is a perspective view illustrating an upper portion of a slidebase for placing two locators together.

FIG. 10A is a side view illustrating an example of a connecting rod forjoining two slide bases.

FIG. 10B is a front view illustrating a locating clamp mechanism for theslide base.

FIG. 11 is a schematic view illustrating methods for placing the locatoron the slide base and for locating the side member to the underbodyusing the locator.

FIG. 12 is a schematic view illustrating a method for replacing thelocators.

FIG. 13 is a schematic perspective view illustrating the posture of thecar body at the roof panel pre-setting station.

FIG. 14 is a schematic perspective view illustrating the roof panelpre-setting station.

FIG. 15 is a schematic side view of the roof panel pre-setting station.

FIG. 16 is a schematic front view of the roof panel pre-setting station.

FIG. 17 is a schematic plan view of the roof panel pre-setting station.

FIG. 18A is a schematic front view illustrating a transfer system forjoisted-locating jigs used at the roof panel pre-setting station.

FIG. 18B is a view illustrating a movable rail of the transfer system ina lower position.

FIG. 19A is a schematic view illustrating a sway prevention mechanismfor the movable rail shown in FIG. 18B.

FIG. 19B is a side view illustrating main parts of the sway preventionmechanism.

FIG. 20A is a front view illustrating falling-out prevention device forpulley, installed at the movable rail shown in FIG. 18B.

FIG. 20B is a view illustrating a stopper of falling-out preventiondevice for pulley, in a release position.

FIG. 21 is a view illustrating a locating clamp mechanism for thejoisted-locating jigs.

FIG. 22A is a front view illustrating the movement of a locatingmechanism provided near the transfer line.

FIG. 22B is a side view illustrating a space to install any additionallocating mechanism.

BEST MODE FOR CARRYING OUT THE INVENTION

As follows, a successful example of this invention is described indetail, with attached drawings being referred.

FIG. 1 is a schematic view illustrating a side member spot weldingstation 1. The side member spot welding station 1 is installed at apredetermined place in a car body assembly line 2 (see FIG. 2). The carbody assembly line 2 includes an underbody loading station (not shown)installed upstream of the side member spot welding station 1 (the leftside in FIG. 2). In this underbody loading station, an underbody 3 isset on coasters 13 a, 13 b (see FIG. 3). Thereafter, the underbody 3,including a rear portion facing downstream of the car body assembly line2 for example, is carried by a roller conveyor 11 (see FIG. 4), to besent to an underbody setting station 5 (#0) and to the side member spotwelding station 1 (#1). The roller conveyor 11 includes a plurality ofrotatable rollers 11 a, each spaced to each other at a predetermineddistance in the transfer direction of the underbody 3 and so on.

As shown in FIG. 2, the downstream side of the side member spot weldingstation 1 (#1) is provided with a roof panel pre-setting station 6 (#2)and a roof panel spot welding station 7 (#3). In the roof panelpre-setting station 6, a roof panel is pre-set on a side member 4, andthe side member 4 is re-spot welded to the underbody 3. A roof panelre-spot welding station (#4) is install next to the roof panel spotwelding station 7 (#3) on its downstream side. When many points of theroof panel is to be re-spot welded, as shown, a plurality of roof panelre-spot welding stations 8-1 (#4)-8-3 (#6) are installed so thatworkload for re-spot welding per one worker is not increased too much.The downstream side of the roof panel re-spot welding station isequipped with a re-spot welding station 9 (#7) having a welding robot,and also equipped with an unloading station 10 (#8).

In the side member spot welding station 1 and the roof panel pre-settingstation 6, the height of the underbody 3 may need to be adjusted tocorresponding types of cars. For this adjustment, each of the stations 1and 6 is equipped with an elevating mechanism for lifting the conveyor11. As shown in FIG. 4B, this elevating mechanism is a pantographmechanism 14, for example. The pantograph mechanism 14 includes aplurality of supporting members 14 a that are pivot-able and joined by apin 14, an air cylinder 14 c, and a sliding mechanism 14 d. The bottomend of one of the supporting members 14 a is reciprocally moved inhorizontal direction by the air cylinder 14 c be means of the slidingmechanism 14 d, thereby lifting and lowering the conveyor 11.

FIG. 5 illustrates the coasters 13 a (13 b) on which the underbody 3 isset. Each of the coasters 13 a (13 b) includes a rectangular base 131for engaging with the rollers 11 a of the conveyor 11. A pair ofbody-receiving parts 133 is installed on the upper surface of the base131 vertically, which is to support the underbody 3. The body-receivingparts 133 are spaced to each other widthwise of the base 131(perpendicularly to transfer direction). The width of the base 131 isshorter than the length of the roller 11 a. One end of the base 131 isequipped with an angle bar 132 fixed by a bolt for preventing thecoaster from moving widthwise during transfer. Another angle bar may befixed at the other end of the base 131.

As shown in FIG. 4A, the coasters 13 a, 13 b are arranged to support thefront and the rear part of the underbody 3. As described above, each ofthe coasters includes two body-receiving parts 133 (see FIG. 5). Thus,the underbody 3 is supported by the coasters 13 a, 13 b at four points.A worker pushes the underbody 3 by hand and convey it on the rollerconveyor 11.

As shown in FIG. 1, the side member spot welding station 1 is equippedwith a plurality of locators 16 for locating left and right side members4. In the illustrated example, two locators 16 are provided for eachside member 4 (see also FIG. 7), and the locators are spaced to eachother in the transfer direction of the assembly line. Each locator 16includes an engaging unit (not shown) for engaging with a predeterminedpart of the side member 4. The engaging unit can be, for example, aclamp mechanism or a suction mechanism. The bottom area of the sidemember 4 is located by the locators 16 when it's spot welded to theunderbody 3. As shown in FIG. 7, the locators 16 are smaller than theside member 4 as seen in the vertical direction (vertical direction inFIG. 7) and in the direction parallel to the transfer direction of theassembly line (lateral direction in FIG. 7).

Each locator 16 is equipped with a lifter 15 including two supportingplates spaced to each other in the transfer direction of the assemblyline. The lifter 15 is movable in the vertical direction. Below eachlifter 15, a slide guide 17 (see FIG. 1) is installed, projecting inparallel to the supporting plate. A slide base 18 is installed on theslide guide 17. The slide base 18 can move reciprocally along the slideguide 17, by worker's manual operation.

The lifter 15 can be lowered (and lifted), while supporting the locator16. The locator 16 set on the lifter 15 is moved downward andtransferred to the lower slide base 18. Thereafter, the slide base 18 ismoved along the slide guide 17 to displace the locator 16 toward theassembly line 2 (forward) or away from the assembly line 2 (backward).

As can be seen from FIG. 6B, 11 and 12, each locator 16 is equipped withfour wheels 20 on its bottom surface. Further, as shown in FIG. 6B,spacers 21 is installed on the bottom surface of the locator 16 foradjusting the height of the locator. On the other hand, spacers 24 thatcontact with the spacers 21 is installed on the top of the slide base18. The locator 16 includes a plurality of vertically extending holes 22at its inside, into which locating pins 25 installed on the slide base18 are inserted. As shown in FIG. 8, the lifter 15 includes a rear endprovided with guards 19 and with a stopper 23 with which the wheel 20contacts for positioning the locator 16 provisionally.

As shown in FIG. 6B, the position X is the upper limit of the lifter 15and the top surface of the lifter 15 is flush with the floor level inthe position X. On the other hand, the position Y is the lower limit.When lowering to the position Y, the locating pin 25 of the slide base18 is inserted into the hole 22 of the locator 16, so that the locator16 is seated on the slide base 18. As can be seen from the figure, thetwo supporting plates of the lifter 15 are spaced to each other at acertain distance enough to prevent interference with the slide base 18during the lowering.

According to the present invention, as shown in FIG. 9, two locators 16may be supported by one slide base 18. In this structure, the slide base18 includes a base 18 a, which is equipped with upright locating pins 25for locating a plurality of locators 16. The base 18 a is furtherequipped with a handle 18 b, which the worker grabs for moving the slidebase 18. As shown in FIGS. 10A and 10B, each locator 16 may also besupported by a respective slide base 18. In this way, the worker can getin between two locators 16 to perform spot welding operation. In theillustrated example, two slide bases 18 are joined to each other bymeans of a removable connecting rod 26. The connecting rod 26 enablesthe worker to move two slide bases 18 together forwards and backwards.The connecting rod 26 may be linear as a whole, but desirably, is acrank having a bending part 26 a between the locators 16, as shown. Inthe form, when the bending part 26 a is positioned downwards (indicatedby solid lines in FIG. 10A), the connecting rod 26 does not obstruct theoperation at the upper area of the side member 4. When working on thelower area of the side member 4, the bending part 26 is positionedupwards (indicated by chain double-dashed lines in FIG. 10A).

As shown in FIG. 10B, the slide base 18 may be provided with a angle 27at the front (at the side facing the conveyor 11), and the angle 27 maycontact with a stopper 28. Desirably, the stopper 28 includes a jaw 30,which is operated by an air cylinder 29. The jaw 30 clamps the angle 27,thereby the slide base 18 is held firmly at a determined position.

The lifter 15 is moved up and down between the above-described positionsX and Y (see FIG. 6B) by, for example, a pantograph mechanism similar tothe one shown in FIG. 4B. When the lifter 15 is lifted to the positionX, its top surface is flush with the floor level. In this position, thelocator 16 with the wheels 20 can be easily moved from the floor ontothe rear end of the lifter 15. Thereafter, as shown in FIG. 11, thewheel 20 contacts with the stopper 23 to position the locator 16provisionally (refer also to the state indicated by reference number 1in FIG. 12). The slide base 18 is installed below the locator 16. Inthis state, when the lifter 15 is lowered (as indicated by referencenumber 2 in FIG. 12), in the middle of lowering the locating pin 25 ofthe slide base 18 is fitted into the hole 25 of the locator 16, wherebythe locator 16 is engaged with and located on the slide base 18. Whenthe lifter 15 is further lowered, the wheel 20 of the locator 16 isdetached from the lifter 15, and the locator 16 is finally seated on theslide base 18.

Next, the locator 16 holds the side member 4 and the slide base 18advances along the slide guide 17 toward the assembly line (as indicatedby reference number 3 in FIG. 3). Then, as illustrated by chaindouble-dashed lines in FIG. 11, the side member 4 is located relative tothe underbody 3 that is on standby. In this state, the side member 4 isspot welded to the underbody 3.

After welding, the fixation of the locator 16 to the side member 4 isreleased and the slide base 18 is retreated at a determined distance (asindicated by reference number 4 in FIG. 12). In this position(hereinafter referred to as “standby position”), the locator 16 holdsnext side member 4 that is to be spot welded to next underbody 3.

When an underbody 3 of a type different from the previous underbody istransferred to the side member spot welding station 1, the previouslocator needs to be replaced with a locator of another type. Theprocedure of the replacement is described below.

First, the slide base 18 and the previous locator 16 are positioned atthe above-described “standby position”, and in this state, the lifter 15is lifted (as indicated by reference number 5 in FIG. 12). Duringlifting, the wheel 20 of the locator 16 rides on the lifter 15, and whenthe lifter 15 is further lifted, the locator 16 is detached from theslide base 18. After the lifter 15 is lifted up to be flush with thefloor level, the wheel 20 is used to move the locator 16 from the lifter15 to the floor level. Thereafter, the locator 16 is returned to alocator stock area near the car body assembly line 2.

After the lifter 15 is lifted and the previous locator 16 is detachedfrom the slide base 18, the slide base 18 is retreated to the rear endof the slide guide 17 (as indicated by reference number 6 in FIG. 12).On the other hand, another locator 16 is set on the rear end of thelifter 15 that is at the upper limit (the position X in FIG. 6B)Thereafter, the lifter 15 is lowered in order to transfer the locator 16to the slide base 18.

The locators used in the above procedure are more compact thanconventional one. Therefore, a plurality (one type or various types) oflocators can be stored near the car body assembly line 2 withoutobstructing the operation. Further, the worker can move the locator 16easily as the wheels 20 are installed on the bottom area of the locator16. On the contrary, conventional large jig is stored at a place apartfrom the car body assembly line 2, and transferred to the side memberspot welding station 1 from the storage, using a special transfer line,if necessary. According to the present invention, such transfer line forjig is unnecessary.

In the example shown in FIG. 1, two locators 16 are used for each sidemember 4, however, the present invention is not limited to this. Forexample, three (or more) locators 16 are used for one side member 4 asshown in FIG. 6A . In this case, each locator may have respective slideguide 17 and slide base 18. Alternatively, a plurality of locators mayshare one elongated slide base.

The underbody 3 and the side member 4 spot welded to each other aretransferred from the spot welding station 1 to the roof panelpre-setting station 6. At the station 6, a roof panel 31 is pre-set andlaid over the top of the side members 4 (see FIG. 13). Further at thestation 6, the underbody 3 and the side members 4 are re-spot welded.The roof panel 31 is pre-set by the worker manually or using any devicesuch as a hoist.

After the pre-setting a roof panel 31, it is spot welded at the roofpanel spot welding station 7. As shown in FIG. 14, the roof panel spotwelding station 7 is equipped with a pair of frames 34 at the sides ofthe transfer line. A pair of removable joisted jigs 35, 36 are installedand laid between the upsides of the frames, being spaced to each otherin the transfer direction. Further, though not shown in the figure, thestation 7 is equipped with a hoist for transferring the jigs 35, 36 andwith a spot welding machine for pre-fixing the roof panel 31 to the sidemember 4. In the illustrated example, though the roof panel 31 isspecified as a part to be fixed to the side member 4, the presentinvention is not limited to this. The present invention can be alsoapplied to fix a part (such as a header inner and a frame back, forexample) to be laid across the side members 4, instead of a roof panel31. Alternatively, reinforcement may be installed across the two frames34.

As shown in FIG. 15, the frame 34 includes vertical bars spaced to eachother in the transfer direction and a horizontal bar connecting thevertical bars. The horizontal bar includes a top surface equipped with aclamp mechanism for installing the removable joisted jigs 35, 36.

As shown in FIG. 16, the joisted jigs 35, 36 include a bottom sideequipped with a pair of clamp arms 39. The clamp arm 39 is operatedmanually or by an air cylinder, for connecting an upper welding end ofthe side member 4 to a welding end of the roof panel 31.

As shown in FIG. 14 or 15, the roof panel 31 is located on the sidemembers 4, whereby a front window opening 40 and a rear window opening41 are formed. According to the present invention, these openings arenot distorted and can be formed as desired. It is because the roof panel31 and the side members 4 are properly located to each other as the roofpanel 31 and the side members 4 are located relatively to a commonimmovable ground. Specifically, the side member 4 is already re-spotwelded to the underbody 3 at the previous station 6. Further, thecoasters 13 a, 13 b supporting the underbody 3 are placed at animmovable system including the ground. Thus, the side member 4 is,though indirectly, fixed to the immovable system. On the other hand, theroof panel 31 can be also fixed to the same immovable system by means ofthe frame 34 (and the joisted. jigs 35, 36). As a result, the roof panel31 and the side members 4 can be firmly located to each other, wherebythe front window opening 40 and the rear window opening 41 can be formedas desired.

As the clamp arms 39 installed at joisted jigs 35, 36 vary with the cartype, different clamps arm 39 are necessary for respective car types. Inthe illustrated example, whole units of joisted jigs 35, 36 includingthe clamps arms are assigned for respective car types, and a pluralityof types of joisted jigs 35, 36 are stored near the car body assemblyline. The joisted jigs 35, 36 are attached to the horizontal bar of theframe 34. Thus, as shown in FIGS. 16 and 17, it is desirable to storethe joisted jigs 35, 36 at platforms 42-1, 42-2 (having height almostthe same as the frame 34) installed adjacent to the car body assemblyline.

The joisted jigs 35, 36 may be stored at one of the platforms 42-1,42-2. In this case, for example, jigs to be attached to the frame 34 arestored at the platform 42-1, and jigs already used and removed from theframe 34 are stored at the platform 42-2. In this way, replacement ofthe jigs can be effectively performed.

The joisted jigs 35, 36 are installed at the front and rear areas ofroof panel 31, with a certain distance between themselves, whichprovides a wide working space. Therefore, welding operation by a workeris much easier, and a spot welding machine and a re-spot welding machinecan be installed in the same area. Further, the easy access to thewelding points enables to use a welding machine with relatively shortreach.

Conventional jigs for roof panel are larger than a roof panel it self,thereby requiring large facility investment and much time for replacingjigs. Contrary, the jigs according to the present invention areelongated and thus don't take much space, thereby not obstructing theoperation even if it is stored near the car body assembly line. Further,as described above, replacement of the jigs is much easier.

FIG. 18A shows a transferring system (indicated by reference number 50)for replacing the joisted jigs 35, 36. As shown, the reference number 51indicates a ceiling rail 51 from which a hoist 52 is hung. The hoist 52elevates and lowers a movable rail (see FIG. 18B). A fixed rail 54 isinstalled below the ceiling rail 51 with a space 55 in between where themovable rail 53 is inserted. The fixed rail 54 is furnished with twostoppers 56 for preventing the movable rail 53 from elevating beyond thefixed rail. The stoppers 56 are installed on the upper surface of thefixed rail 54 and protrude horizontally from the end of the fixed rail.As shown in FIG. 18A, the movable rail 53 and the fixed rail 54 arejoined and form, as a whole, one transfer path. In the illustratedexample, two pulleys 57 connected each other can move along the transferpath. For connecting two pulleys 57, a rod of a predetermined rigidityor other material can be used (this structure can give a certain spacebetween two pulleys 57). The joisted jig 35 (36) is hung from thepulleys 57. The pulleys 57 can move along the path of the movable rail53 and the fixed rail 54.

As shown in FIG. 18A, the pulleys 57 with hung joisted jig 35 (36) istransferred along the fixed rail 54 to the movable rail 53. Thereafter,as shown in FIG. 18B, the movable rail 53 is lowered by the hoist 52,and the joisted jig 35 (36) is positioned on the frames 34. A rail swayprevention mechanism 60 as shown in FIGS. 19A, 19B is furnished forpreventing the movable rail 53 from swaying while lowering the joistedjig 35 (36). The illustrated mechanism 60 includes a fixed guide 61installed on and hung from the ceiling, an upright bar 62 installed onthe movable rail 53, and a rotatable roller 63 installed at each uprightbar 62. As shown in FIG. 19B, the roller 63 rolls at the inner wall ofthe fixed guide 61 as the upright bar 62 moves up and down.

When the movable rail 53 is lowered (see FIG. 18B), the pulleys 57 mayfall out of the movable rail 53. To prevent the falling, for example,stopper levers 58 are provided as shown in FIGS. 20A, 20B. The stopperlever 58 turns on the pivot, and when the movable rail 53 is lowered,the stopper lever 58 takes a position as shown in FIG. 20A due tobiasing force of a spring (not shown). As shown in FIG. 20B, when themovable rail 53 is lifted up and fits in the space 55 of the fixed rail54, the upper end of the stopper lever 58 is pushed down by the stopper56. In this way, the stopper 58 lever is brought into a horizontalposture, whereby the pulley 57 can move from the movable rail 53 to thefixed rail 54, and vice versa.

FIG. 21 illustrates a locating mechanism 70 for attaching the joistedjig 35 (36) to the frame 34. In the illustrated example, a locating pin71 protrudes from the top surface of the frame 34, while the joisted jig35 (36) includes a hole 72 in which the locating pin 71 to be inserted.After the locating pin 71 fits in the hole 72, a clamp arm 73 is used tofix the joisted jig 35 (36) to the frame 34.

FIGS. 22A and 22B illustrate a locating mechanism 80 which may beinstalled near the car body assembly line. The mechanism 80 includes anupper part 81 and a lower part 82, and the lower part 82 is fixed to thefloor while the upper part 81 is rotatable and joined to the lower part82 with a pin 83. As shown in FIG. 22A, the lower part 82 is equippedwith an air cylinder 84, while the upper part 81 is connected to a driverod of the air cylinder 84. The upper part 81 can be placed at avertical position (illustrated by solid lines) or an inclined position(illustrated by broken lines) by moving the drive rod out from and intothe main body of air cylinder. The upper part 81 is furnished with twospacers 85 and one locating pin 86.

As described above, the inclining upper part 81 prevents theinterference between an object transferred along the assembly line andthe locating mechanism 80. In case, for example, of a coaster 13 c thatincludes body-receiving parts 133 a protruding in lateral direction asillustrated by chain double-dashed lines in FIG. 22A, the inclinedposition of the upper part 81 enables proper transfer of the coaster 13c along the assembly line without being obstructed by the locatingmechanism 80.

According to the present invention, in addition to the above-describedlocating mechanism 80, another locating mechanism of different type maybe installed. In this case, as shown in FIG. 22B, the additionalmechanism can be installed at a space S near the mechanism 80 (or anyother place).

The present invention being thus described, it is obvious that the sameinvention can be modified in various ways. Such modifications should notbe regarded as a different idea from this invention or to be out of itsscope, and all such modifications as would be obvious to those skilledin the art are intended to be included in the scope of the appendedclaims.

1. A method of assembling a car body by spot welding a bridging part toa pair of side members fixed to an underbody of a car, the methodcomprising: installing a pair of fixed frames at sides of a bodytransfer line for transferring the underbody and the side members;attaching a plurality of joisted-locating jigs to the fixed frames forlocating the side members and the bridging part, the plurality ofjoisted-locating jigs being spaced from each other in a transferdirection of the underbody; and spot welding the side members to thebridging part, with the side members and the bridging part clamped bythe plurality of joisted-locating jigs; wherein a first stock area isprovided on one side of the body transfer line while a second stock areais provided on an opposite side of the body transfer line, the bodytransfer line and the pair of fixed frames being interposed between thefirst and second stock areas; and wherein a transfer system is employedto convey each of the plurality of joisted-locating jigs along a jigtransfer line extending above the fixed frames transversely of the bodytransfer line, from the first stock area to the fixed frames forattachment thereto and from the fixed frames to the second stock areafor replacement with other joisted-locating jigs which are also conveyedfrom the first stock area to the fixed frames.
 2. The method ofassembling a car body according to claim 1, wherein the fixed frames andeach of the plurality of joisted-locating jigs are located and fixed bya clamp mechanism.
 3. The method of assembling a car body according toclaim 1, wherein the transfer system includes a motor, a movable railmoved up and down by the motor, a fixed rail to be combined with themovable rail, and a pulley movable along the movable rail and the fixedrail, each of the plurality of joisted-locating jigs being hung from thepulley, the fixed rail and the movable rail extending in a directioncrossing the transfer direction of the underbody.
 4. The method ofassembling a car body according to claim 3, wherein a sway preventionmechanism is furnished for preventing the movable rail from swaying whenthe movable rail and the fixed rail are disconnected.
 5. The method ofassembling a car body according to claim 4, wherein the sway preventionmechanism includes a pair of vertical rods attached to the movable railand a pair of fixed guides fixed to an immovable structure, the verticalrods being movable relative to the fixed guides via a roller.
 6. Themethod of assembling a car body according to claim 3, wherein a fallprevention mechanism is provided at the movable rail for preventing thepulley from falling out of the movable rail.
 7. The method of assemblinga car body according to claim 6, wherein the fall prevention mechanismincludes a stopper that turns on the predetermined pivot, the stopperbeing movable between a position at which the stopper engages with thepulley and a position at which the stopper is disengaged from thepulley.